1. Field of the Invention
The present invention relates to a superconductor mixer and a phase control method therefor provided a non-linear element operative at a temperature of liquid nitrogen or lower, having a frequency converting function (mixer function) in a wide band frequency region and a phase control function, and thus is suitable for a phased-array antenna.
2. Description of the Prior Art
For promoting application of superconductor for electronic devices, high frequency response of the superconductor is quite important. There has been a demand for development of a superconductor mixer of higher frequency response and higher sensitivity. Conventionally, a superconductor mixer relatively easily performing mixer operation at a frequency near 100 GHz or higher has been practicable. On the other hand, as to phase control for the superconductor, separately from development of the mixer function, there has been developed a system which has an only function of phase control. For example, a phase control pattern, in which one signal line is separated into two signal lines having mutually different line lengths and then re-combine them, is considered. Means for blocking the signal propagating the signal line is provided on the separated signal lines. A phase is controlled by propagating a signal through the respective signal lines and blocking the signal propagating on one signal line.
On the other hand, as a phase control method, there is a method for controlling a phase by applying a current to several hundreds of reticular Josephson junction elements so that a current at respective Josephson junctions may be greater than or equal to the critical current for varying a reactance of the overall element (1992, IEEE MTT-S Digest 469-472).
In the conventional methods set forth above, the portion to block the signal or the several hundreds of Josephson junction elements are required to be formed on the same substrate. Formation of these is quite difficult. Also, since a portion performing mixer operation has to be formed on another portion, the superconductor mixer with the phase control function requires large area and is difficult to reduce the size.
On the other hand, as a prior art, there is a technology, in which a semiconductor of a variable resistance by irradiation of a light is arranged between two superconductive lines. In this technology, by adjusting a light to be irradiated on the semiconductor, a resistance of the semiconductor can be varied to selectively pass and block the signal between two superconductive lines. This method requires the semiconductor device arranged between two superconductive lines. Also, means for guiding the light to the semiconductor device is necessary. Therefore, the device cannot be formed only with superconductor. On the other hand, such a pattern does not has a frequency converting function, and thus requires the mixer to be formed independently in another portion.